With your heroes I would definitely try the following arrangements
Lots of intriguing options. You have a lot of very strong defense characters.
Zimkitha-Fast speed AOE, cleanse and attack buff (and heal for red). She does so many different useful things. Hard not to include her
GM-one of the best defense characters in the game. He very quickly melts through multiple targets at very fast speed.
Alasie-one of the best defensive snipers. Good stats, hits hard and the mana generation debuff is very useful
Morgan Le Fay-I think she’s great on defense as the undispellable life steal is extremely strong.
Guin-one of the top tanks
Ursena-I like her best at tank. She could be a decent flank but I think you have better options. At tank she can combo with Ranvir’s buff and do some crazy damage
Kage-speed is king and very fast rules them all. Solid sniper.
I think I prefer the first setup I mentioned. You get the nice elemental link synergy with Zimkitty and GM. You get nice tank/Flank color synergy with the yellow tank/purple flank (Kage). Take your pick of Alasie/MLF for the last spot, both are fantastic